Dissolved oxygen in milk and dairy products

Anton Paar Australia Pty Ltd
Sunday, 01 September, 2024

Dissolved oxygen (DO) in dairy products is a critical quality parameter affecting the nutritive value, colour, taste and shelf life of dairy products. During pasteurisation DO has to be removed from the milk to improve process performance and to secure consistent quality of the final product. To assure your product contains the target DO content, Anton Paar’s inline oxygen sensors Oxy 4100 Transmitter and Oxy 5100, can be easily integrated directly into your production line. Customers benefit from an accurate and reliable DO monitoring for a wide range of concentrations.

1. Milk pasteurisation process

The milk pasteurisation process consists of a series of process steps, which transform non-sterile raw milk into a sterile product. On arrival at the dairy processing plant, the milk will contain an equilibrium amount of approx. 8 ppm DO and finely dispersed air as a result of transportation. During the processing and in the final package the DO content should be lower. Deaerators are used to remove dispersed air and reduce the oxygen (O2) content to a target value of 0–3 ppm. Typically, this is done before the temperature treatment to improve efficiency of heating and to minimise the oxidation rate during the high temperature processing. Deaeration also prevents foaming, maintains constant filling and reduces fouling, development of stale flavour and loss of O2-sensitive ingredients (vitamins C and B9).

2. Application of the Oxygen Sensors

To assure the goal of deaeration has been accomplished the concentration of DO must be measured. The oxygen sensor Oxy 4001 Transmitter or Oxy 5100 easily detects any deviations from the target DO value. This allows adjustments of deaeration to correct the production process (e.g. by increasing vacuum when the measured values are too high). The sensor should be installed after the deaerator at the pressure side of the pump (Figure 1).

Installing the sensor prior to packaging enables the last check of the DO values before the product is filled into its final package.

Dairy products to be measured

The oxygen sensors Oxy 4100 and Oxy 5100 are suitable for DO monitoring in

any kind of milk
flavoured milk drinks and milk smoothies
sour milk products (i.e. soured milk, kefir, yoghurt, cream yoghurt, buttermilk)

Comparing Lab and Process Instrumentation

Results of the inline process measurement are in good agreement with the lab reference. This enables precise real-time control of the DO content in milk during production. Figure 2 illustrates the correlation of process (Oxy 5100) and lab (OxyQC Wide Range) instrument data obtained for pasteurised milk (3.5% fat) for a wide range of DO concentrations.

Sudden changes (Figure 2) of the DO concentration results from the harsh concentration adjustments in the test system.

3. Measurement Setup

Anton Paar’s oxygen sensors Oxy 4100 Transmitter and Oxy 5100 are based on the fluorescence phase shift and enable measurements over a wide range of DO concentrations (0–45 ppm) based on a fluorescence phase shift.

The sensors consist of a luminescent dye (O2-sensitive layer) which is in direct contact with the measured fluid sample). The measurement setup of the sensor is shown in Figure 3.

A light-emitting diode (LED) of suitable wavelength sheds light on the O2-sensitive luminophore, which is excited by absorbing light. A part of this absorbed light is released by emitting fluorescent light at a higher wavelength. In the presence of O2 as the quencher molecule, a fluorescence phase-shift between excitation of the luminophore and fluorescence emission occurs. The sensor detects this fluorescence quenching, and the resulting phase shift is a direct measure of the DO content.

Anton Paar’s oxygen sensors, the Oxy 4100 Transmitter and the Oxy 5100 (Figure 4), can be easily implemented directly into the production line with a VARIVENT® Type N process connection. Easy process integration in combination with the robust and hygienic design makes the oxygen sensor a minimum maintenance device.